Cell cycle regulation plays a critical role in neoplastic disease, as well as disease caused by non-cancerous, pathologically proliferating cells. Normal cell proliferation and progress through the phases of the cell cycle (G1, S, G2, and M, also the G0 state) is tightly regulated by the activation and deactivation of a series of proteins that constitute the cell cycle machinery. The expression and activity of components of the cell cycle can be altered during the development of a variety of human disease such as cancer, cardiovascular disease, psoriasis, where aberrant proliferation contributes to the pathology of the illness. There are genetic screens to isolate important components for cell cycle regulation using different organisms such as yeast, worms, flies, etc. However, involvement of a protein in cell cycle regulation in a model system is not always indicative of its role in cancer and other proliferative disease. Thus, there is a need to establish screening for understanding human diseases caused by disruption of cell cycle regulation. Identifying proteins, their ligands and substrates, and downstream signal transduction pathways involved in cell cycle regulation and neoplasia in humans is important for developing therapeutic regents to treat cancer and other proliferative diseases.